Re: [PATCH 0/4] mm/hugetlb: Early cow on fork, and a few cleanups

[Gal Pressman <galpress@amazon.com>]

On 03/02/2021 23:08, Peter Xu wrote:
> As reported by Gal [1], we still miss the code clip to handle early cow for
> 
> hugetlb case, which is true.  Again, it still feels odd to fork() after using a
> 
> few huge pages, especially if they're privately mapped to me..  However I do
> 
> agree with Gal and Jason in that we should still have that since that'll
> 
> complete the early cow on fork effort at least, and it'll still fix issues
> 
> where buffers are not well under control and not easy to apply MADV_DONTFORK.
> 
> 
> 
> The first two patches (1-2) are some cleanups I noticed when reading into the
> 
> hugetlb reserve map code.  I think it's good to have but they're not necessary
> 
> for fixing the fork issue.
> 
> 
> 
> The last two patches (3-4) is the real fix.
> 
> 
> 
> I tested this with a fork() after some vfio-pci assignment, so I'm pretty sure
> 
> the page copy path could trigger well (page will be accounted right after the
> 
> fork()), but I didn't do data check since the card I assigned is some random
> 
> nic.  Gal, please feel free to try this if you have better way to verify the
> 
> series.

Thanks Peter, once v2 is submitted I'll pull the patches and we'll run the tests
that discovered the issue to verify it works.